1. Field of the Invention
This invention relates to an injection molding machine of the type which operates with at least two melting and injector units, the injection molding machine including a movable die platen that mounts a half part of an injection mold and is movable on fixed spars, a fixed die platen that mounts a half part of an injection mold, and a prismatic support base which can be pivoted around its axis between these half-mold parts on the movable die platen and the fixed die platen and which is movable in parallel with the elongation dimension of the fixed spars, the side surfaces of the support base which extend in parallel with its axis including the complementary half parts of the injection molds to the half parts on the movable die platen and the fixed die platen.
2. The Prior Art
Injection molding machines which operate with two melting and injector units and which include a prismatic support base are known--see German Auslegeschrift No. 12 15 353.
To inject plasticized material, the half-mold parts on the two die platens (which always face one another) and those on the prismatic support base are brought together to create closed (complete) injection molds, one of the injection molds having a broken mold core that has been extruded in the previous injection molding cycle and the other injection mold being empty. After injecting melted material, which occurs simultaneously from the two melting and injector units, one of the injection molds will have a finished jet molded part while the other injection mold will contain a broken mold core. The injection molds are then opened by appropriately moving the movable die platen along the fixed spars. Since tension springs are located between the die platens and the guides for the prismatic support base on the spars, the injection molds open automatically when the movable die platen is appropriately moved. When the injection molds open, the prismatic support base can be pivoted in such a way that the broken mold core together with its half-mold part assumes the position of the half-mold part with the broken mold core from the previous injection cycle. Subsequently, an appropriate shift of the movable die platen, while the injection mold is being created, will cause the half-mold parts located opposite one another to be in a closed position while material is again injected, so that a finished injection molded object and a broken mold core are again extruded simultaneously.
By processing different types of plastic materials with the two melting and injector units, molded objects can be produced which differ, for instance, with regard to material characteristics and color.
One of the melting and injector units, together with the movable die platen, forms a movable component which is guided along the spars, while the other melting and injector unit works in conjunction with the fixed die platen.
To open and close the injection molds formed by the respective half-mold parts, a toggle lever serves as closing unit, the toggle lever being controlled by the movable melting and injector unit and by the frame of the machine and can also be acted upon by a working hydraulic cylinder.
The axis of the prismatic support base is positioned in such a way that it can be rotated within two bearing sleeves which are positioned on the fixed spars in such a way that they can be moved. Between these two spars and the die platen are the tension springs.
The prismatic support base, when viewed in cross section transverse to its axis, exhibits the outline of a regular octagon, whereby its side surfaces, which extend in parallel with its axis, support half-mold parts and its axis is horizontal and perpendicular to the direction of its movement, i.e., perpendicular to the elongation direction of the spars.
However, these injection molding machines have significant disadvantages. For example, the mass moved on the spars is too great. In this regard, it is in general desirable in such injection molding machines to keep the kinetic energy of the mass to be moved on the spars as low as possible since the total mass in one end position, i.e., the maximum opening of the injector machines, should be accelerated as rapidly as possible from the resting position to a preset maximum speed, which is then held constant until it reaches the mold closing control point. From this point on the entire mass is decelerated in such a way that the mold forms are closed while moving at a crawl. It seems obvious that when injection cycles are as brief as possible and distances over which the total mass is accelerated from the rest position to maximum speed are as short as possible and the remaining distance from the mold-closing control point to the closing of the mold is as short as possible, the mass to be accelerated should also be as small as possible.
However, reducing the total mass that must be moved in such injection molding machines is not by itself sufficient since the support base together with its collet and tension springs between the die platens forms a muffled system that can oscillate in the course of its dynamic movements, and since its half-mold parts bounce against the mold parts of the die platens as soon as the available time is too short for the injection cycles, so that the injection cycles of these injection machines is too long in comparison to the injection cycle of modern machines in which only the half-mold parts of injection molds are placed between their die platens. This is apparently one of the reasons why such injection molding machines with an additional prismatic support base between the die platens have not been accepted.
Against the background of these considerations, the present invention addresses the problem of designing this type of an injection molding machine in such a way that the closing of the injection molds is assured while moving at a crawl, and in such a way that the injection cycles are kept as short as possible.
The invention furthermore addresses the problem of designing such injection molding machines in such a way that molded articles can be created in which more than two sections are made of plastic materials with different properties and/or different colors or shades of color, or in which areas alternate between being transparent and opaque.